The production of red amorphous phosphorus by the thermal conversion of yellow phosphorus is well known. In one commercial operation, such conversion is achieved by heating a batch of yellow phosphorus in an enclosed container until thermal conversion commences at about 270.degree. to 280.degree. C., thermal conversion is allowed to occur while cooling air or the like is used to remove the heat of conversion until the exotherm subsides, the container is further heated to a temperature of about 370.degree. to 380.degree. C. to achieve further conversion of the yellow phosphorus to red phosphorus, and the container then is cooled to room temperature, opened and the red phosphorus recovered.
The latter operation is a time consuming one, typically involving about 100 hours for each batch, and does not result in complete conversion of yellow phosphorus to red phosphorus, so that precautions must be taken to avoid release of unconverted yellow phosphorus to the atmosphere and provision for disposal of unconverted yellow phosphorus must be provided. In addition, the red phosphorus is obtained in the form of a hard cake-like compact mass which requires considerable mechanical action to remove the same from the container and to reduce it to particulate form.
Efforts have been made to improve on this prior art procedure, in particular to improve the efficiency of conversion of yellow phosphorus to red phosphorus and to provide the process as a continuous one, but to date none of these improvements have reached commercial operation. Representative patents covering such processes are U.S. Pat. Nos. 4,152,403 and 4,188,367.